Recently, mobile phones have been widely used by the public. The mobile phone was once used only for voice calls, but now there are more various functions and recently released mobile phones support short messaging and multimedia messaging functions. More recently, so-called smart phones are widely used. Smartphones provide users with various functions such as web browsing, gaming, and map service. In order for users to enjoy and find convenient the functions of smartphones, there is an inevitable need for support for high speed data communication.
Recently, the 3rd Generation Partnership Project (3GPP) completed standardization of most parts of Long Term Evolution (LTE). In some countries, commercialized LTE services have been launched already. LTE communication technology supports much faster data communication than Wideband Code Division Multiple Access (WCDMA) communication technology. The present invention is directed to a communication system complying with the LTE standard. However, it is obvious that the present invention can be applied to other communication systems without departing from the spirit of the present invention. Although the term “evolved node B” (eNB) is used to mean “base station” in the present invention, the present invention can be applied to other systems operating with various types of base stations such as node B, Radio Network Subsystem (RNS), Base Transceiver Station (BTS), and wireless access point.
In LTE, a Radio Resource Control (RRC) protocol is used to allocate radio resources to the users. The RRC protocol takes charge of allocating radio resources to the user in need of communication and withdrawing the resources allocated but not in use by the user.
That is, the RRC protocol is a protocol for use in managing the radio resources allocated to User Equipment (UE) within a cell. According to the RRC protocol, the UE can be in two different states: RRC_IDLE and RRC_CONNECTED. The RRC_IDLE state is a state in which the UE has not been allocated radio resources from an eNB or a connection between the UE and the eNB has been released. The RRC_CONNECTED state is a state in which the UE has been allocated radio resources from the base station. In the RRC_CONNECTED state, the UE may transmit data in uplink and the eNB may transmit data in downlink.
If the UE has data to transmit or receive, it has to transition to the RRC_CONNECTED state. The UE in the RRC_CONNECTED state occupies more resources than the UE in the RRC_IDLE state. Accordingly, if there are too many UEs in the RRC_CONNECTED state among the UEs served by an eNB, the eNB is likely to undergo a call drop or call blocking situation. Thus the eNB monitors the traffic of the UEs to detect the UE in a so called non-communication state. In the case that there is no uplink or downlink traffic between the UE and the eNB over a predetermined time period, the eNB releases the connection of the corresponding UE to mitigate any resource shortage problem. This technique is referred to as User Inactivity Control Function or UE connection management method.